Silicone hydrogels have been prepared by polymerizing mixtures containing at least one silicone containing monomer and at least one hydrophilic monomer. Either the silicone containing monomer or the hydrophilic monomer may function as a crosslinking agent or a separate crosslinking agent may be employed. Various alcohols, including n-hexanol, ethanol, and n-nonanol have been used as diluents to compatibilize the silicone monomers and the hydrophilic monomers. However, the articles made from these components and diluents either did not form clear articles or were not sufficiently wettable to be used without a coating.
Primary and secondary alcohols having more than four carbon atoms have also been disclosed to be useful as diluents for silicone containing hydrogels. However, many of these diluents do not form clear, wettable articles when internal wetting agents are included in the reaction mixture. While these diluents are useful, many require an additional compatibilizing component to produce clear, wettable molded articles. Thus, there still remains a need in the art for silicone hydrogels which are polymerized in an economic and efficient way which may yield medical devices such as clear contact lenses. Silicone hydrogels comprise hydrophobic and hydrophilic compounds that have an inherent propensity to dissociate from each other. It is believed, without being limited to this mechanism, the observation of haze in lenses is likely attributable to the presence of phase separation on a scale that results in scattering of transmitted light. An imbalance in the polymerization rates or molar ratios of components may result in formation of blocks rich in one monomer, which may form haze.
Some commercially available silicone hydrogel lenses, such as Focus N&D (by Ciba Vision) and Purevision (by Bausch and Lomb) require specialized treatment in manufacture to impart surface wettability. The present invention produces silicone hydrogel lenses which contain internal wetting agents and do not need surface modification for surface wettability (lubricity) and clarity (lack of haze, as described below).